Signal transmission system



May 14, 1963 A. H. LORD 3,090,031

SIGNAL TRANSMISSION SYSTEM Thai. 7

Filed Sept. 29, 1959 rsaurce L96 L6 m6 K #04 3,090,031 SIGNAL TRANSMISSEON SYSTEM Arthur H. Lord, Houston, Tex, assignor to Texaco Inc, New York, N.Y., a corporation of Delaware Filed Sept. 29, 1959, Ser. No. 843,110 Claims. (Cl. 340-18) This invention relates to an electrical transmission system and, more particularly, to a system for transmitting electrical signals from a signal source located at one end of a string of pipe to a receiving device located at the other end thereof.

An object of the invention is to provide an improved system for transmitting signals through a plurality of interconnected drill pipes forming a string of drill pipe or tubing from a downhole unit located at the lower end of the string to a receiving unit located at the earths surface.

Another object of this invention is to provide a borehole signal transmission system which does not require a continuous cable or wire to be passed through the entire length of the pipe string or which does not require splicing a cable or wire at the joints of the string of drill pipe as the latter is being made up.

In oil field operations, it is often desirable to simultaneously drill a borehole and log the formation traversed by the borehole. In the logging while drilling operation an exploring unit must be located in the drill pipe and, preferably, in a drill collar near the drill bit. The exploring unit may be of the type used for determining radio'- activity, resistivity, self potential, borehole inclination, temperature, pressure, etc. In prior art logging while drilling operations, the exploring unit is connected electrically to a receiving device located at the earths surface, such as, to a meter or recorder, or the exploring unit is housed in a self-contained unit, located near the drill bit, which also houses the receiving device. When an exploring unit is connected to a receiving device located at the earths surface, signal transmission has been accomplished by passing a cable containing one or more wires throughout the length of the string of pipe or by providing each pipe section with a separate length of cable and interconnecting or splicing the ends of these cables when the pipe string is made up. It is, of course, extremely difficult to pass or thread a continuous cable through a long pipe string when the sections are being joined, and in those cases where the cable is spliced at the joints of the pipe sections a considerable amount of time is consumed before the entire circuit is completed, and when the pipe .string is being taken out of the hole, the splices must be broken.

In US. Patent 2,379,800 granted to D. G. C. Hare, a borehole signal transmission system has been disclosed which eliminates the necessity of threading a cable through a string of metallic pipe or of splicing wires as the pipe string is being made up. The transmission system disclosed in the above-mentioned patent includes a first coil or winding disposed at one end of a pipe and a second coil or winding disposed at the other end of the pipe, one end of one of the two coils is connected to one end of the other of the two coils by an insulated wire, the other end of each of the two coils being interconnected through the metallic pipe. When two pipes equipped with this circuit are joined, two coils, one in each of the two pipes, are brought together to form a transformer coupling between the two pipes. Although this patented system has many desirable features, it has been found that relatively high losses are encountered at each of the transformers in the pipe string. High temperatures and pressure, conductive mud and the electrical and magnetic properties of drill pipe form an unfriendly environment for the transformers.

3,%,3l Patented May 14, 1963 In accordance with the present invention, each pipe or section of a pipe string is provided with an electrical circuit which includes a coil or winding disposed at each end of the section, a semi-conductor device for amplifying signals entering into the section through one of the coils and a source of energy coupled to the semi-conductor device. When the pipe string is made up the windings in the adjacent ends of two adjoining sections form a circuit which can pass a relatively strong signal from one pipe section to the succeeding section. By employing a plurality of these pipe sections a long continuous signal transmission circuit is simply and inexpensively provided between a downhole unit and a receiving unit at the earths surface spaced apart by thousands of feet.

For a better understanding of the invention, reference may be had to the accompanying drawing in which:

FIG. 1 is a vertical sectional view through a borehole illustrating the apparatus of the present invention,

FIG. 2 is a vertical sectional view taken through a portion of two adjacent sections of a pipe string at the coupling thereof, and

FIG. 3 is a plan view showing the box end of one of the two pipe sections illustrated in FIG. 2 of the drawing.

Referring to the drawing, FIG. 1 shows a borehole 10 traversing subsurface formations 12, 14 and 16 which contains borehole drilling apparatus. The apparatus includes a string of drill pipe 18, generally steel pipe, having at least pipe sections 20*, 22, 23 and 24, a drill collar 26, a drill bit 28 and conventional pipe string rotating means 30 located at the earths surface. A signal source 32 is located within the drill collar 26, the output of the signal source 32 is connected to a primary winding 34, disposed at the upper end of the drill collar 26, of a first transformer 36 by means of a first insulated wire 38 and the drill collar 26. A secondary winding 40, located at the lower end of the pipe section 20, of the transformer 36 is connected directly to a first transistor 4-2 located in the pipe section 20 in the proximity of the secondary winding 46, one terminal of the secondary winding 40 being connected to the base and the other terminal of the winding 41 being connected to the emitter of transistor 42. The output from the transistor 42 is connected to a primary Winding 44 located at the upper end of the pipe section 20, of a second transformer 46 through a second insulated wire 48, the pipe section 26 and a first source of electric energy 50, the source of energy 50 being effectively connected between the emitter and the collector of the transistor 42. A secondary winding 52, located at the lower end of the pipe section 22, of the second transformer 46 is connected between base and emitter of a second transistor 54. The output of the second transistor 54 is connected to a primary winding of a transformer (not shown) located at the upper end of the pipe section 22. The pipe section 24 is disposed near the earths surface and additional pipe sections, such as pipe section 23, similar to the pipe sections 20 and 22, and containing similar circuitry, may be inserted between the pipe section 22 and 24. A secondary winding 56, located at the lower end of pipe section 24, of a third transformer 58, which has a primary winding 66 disposed in the upper end of pipe section 23, is connected between the base and emitter of a third transistor 62. The collector of the third transistor 62 is connected to a slip ring 64 of a slip ring connector 66 by means of a wire 68. The emitter of the third transistor 62 is connected to the slip ring 70 of the slip ring connector 72 through the pipe section 24. The slip ring 64 of the slip ring connector 66' is insulated from the pipe section 24 but the slip ring 70 of the slip ring connector 72 is electrically connected to the pipe section 24-. Each of the transistors 42, 54 and 62 are preferably silicon transistors which have been found to be relatively stable under high temperature and pressure conditions encountered in a deep borehole. A utilization device 74 which may include a meter or recording instrument is connected to the slip ring 64 through a brush 76 of the slip ring connector 66 and to the slip ring '70 through a brush 78 of the slip ring connector 72. lf desired, a capacitor may be inserted between each secondary coil and the base of each transistor for tuning purposes.

As shown in FIG. 2 of the drawing, the electrical elements disposed at each end of the pipe sections may be formed, preferably, as an annular cast unit which includes a winding and at least one other element imbedded therein, i.e., energy source or transistor, of the circuit in each pipe section. The unit 80 supported within the pin end of a pipe section shown in FIG. 2. may contain a Winding 82, similar to one of the windings illustrated in FIG. 1, and a transistor 84, as illustrated in FIG. 1. The unit 86 located in the box end of a pipe section shown in FIG. 2, may contain a winding 88 and a battery 90, which may be similar to those illustrated in FIG. 1. The units 80 and 86 may be cast in an epoxy resin and formed so as to provide an open center for mud flow and at least two lugs 92 and 94 on the unit 80 and 96 and 98 on the unit 86. The external diameter of each cast unit is such that the unit can be inserted into the pipe in a press-fit. In order to more firmly secure the units 80 and 86 in the drill string, the conventional pipe sections may be modified slightly by providing two bayonet-type slots ran and 102 in the pin end of the pipe section and two bayonettype slots 104 and 106 in the box end of the pipe section shaped to receive the lugs 92 and 94, and 96 and 93, respectively, of the cast units 8t] and 86. Electrical connections between the elements in the cast units 86 and 86 may be made before the casting operation has been performed. Each of the wires passing through the pipe sections, for example, wires 38, 48 and 68 shown in FIG. 1 or Wires 110 and 112 shown in FIG. 2, may be disposed in shallow longitudinal recesses or grooves in the pipe sections such as shown at 114 and 116 in FIG. 2 and, if desired, covered with a layer of epoxy resin. Each end of the Wires 38, 48 and as may be terminated at a point in a bayonet-type slot, such as point 198 in slot 106 as shown in FIG. 3, so as to come into electrical contact with an electrical terminal of a cast unit when the unit is in its locked position within the slot. The other electrical terminal of the cast unit may be made to contact any desirable point at a threaded end of the pipe section.

The unfriendly environment for electrical circuitry in a borehole drill stem causes the energy output from any one of the transformers 36, 46 or 58 located at the joints between adjacent sections to be only a small fraction of the input energy to the respective transformer. However, due to the unique characteristics of transistors, particularly the silicon junction transistors, the energy lost at the transformers may be readily replaced by inserting into a drill pipe one of the transistors and an appropriate source of energy therefor without causing a substantial decrease in the mud flow through the pipe. Transistors have excellent voltage and power amplification with total power-supply requirements in the order of 1.5 to 3 volts. Furthermore, the transistor circuits in the pipe sections may be readily designed so that power consumption occurs only in the presence of a signal. Such moderate power demands can be satisfied in a number of ways in the pipe section. For example, standard mercury-type penlight batteries may be used which satisfy power demands for several months of continuous operation, thus reducing battery replacement to an insignificant factor. If desired, the power may be supplied by the introduction of small quantities of chemical additives to the drilling mud and/or proper choice of metallic compounds to comprise battery poles at the location of each transistor to provide battery power by electrolytic action. Also, a simple thermocouple pile arrangement can be provided to supply the necessary electric power to the transistors at each transformer.

A wide variety of signals may be transmitted through the string of drill pipe from the signal source 32, however, from the standpoint of transfer efiiciency and battery life, short duration pulses are preferred.

Accordingly, it can be seen that a signal transmission system has been provided for borehole drilling apparatus which will readily transmit signals from a signal source located in a deep borehole to utilization equipment located at the earths surface without the necessity of providing a metallic connection in the signal transmission circuit at each coupling between adjacent pipe sections. Thus, the string of drill pipe may be made up or broken without any delays due to the presence of a signal transmission system in the drill string.

Although the invention has been described in connection with borehole drilling apparatus, it should be understood that the invention may be used in connection with any string of pipe which is composed of intercoupled pipe sections.

Obviously, many modifications and variations of the invention as hereinabove set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In a system for drilling a borehole in the earth comprising a drill string having a drill bit at one end thereof, said drill string including a plurality of sections of drill pipe joined to one another end to end, logging apparatus mounted in the vicinity of said drill bit, and a signal transmission circuit electrically coupling said logging apparatus through said sections of drill pipe to surface electrical equipment at the end of said drill string remote from said drill hit, each of said sections of drill pipe having a first coil disposed at one end thereof and a second coil disposed at the other end thereof, the first coil of one pipe section and the second coil of an adjacent pipe section being inductively coupled to one another thereby comprising a transformer, circuit means coupling said first coil to said second coil within said section of drill pipe, each of said circuit means including a semiconductor amplifier having an input coupled to one of said coils and an output coupled to :the other of said coils, said first coil and said semi-conductor amplifier being imbeddcd within a first annular unit formed essentially of epoxy resin and fitted closely within said one end of each of said sections of drill pipe, and said second coil being imbedded within a second annular unit formed essentially of epoxy resin and fitted closely within said other end of each of said sections of drill pipe.

2. In a system for drilling a borehole in the earth comprising a drill string having a drill bit at one end thereof, said drill string including a plurality of sections of drill pipe joined to one another end to end, logging apparatus mounted in the vicinity of said drill bit, and a signal transmission circuit electrically coupling said logging apparatus through said sections of drill pipe to surface electrical equipment at the end of said drill string remote from said drill hit, each of said sections of drill pipe having a first coil disposed at one end thereof and a second coil disposed at the other end thereof, the first coil of one pipe section and the second coil of an adjacent pipe section being inductively coupled to one another thereby comprising a transformer, circuit means coupling said first coil to said second coil within each of said sections of drill pipe, each of said circuit means including an amplifier comprising a transistor having an emitter, a collector and a base, said first coil being connected between the emitter and the base of said transistor and a source of energy being connected between the collector and emitter of said transistor through said second coil, said first coil and said transistor being imbedded within a first annular unit formed essentially of epoxy resin and fitted closely within said one end of each of said sections of drill pipe, and

said second coil and said source of energy being imbedded Within a second annular unit formed essentially of epoxy resin and fitted closely within said other end of each of said sections of drill pipe.

3. In a system for drilling a borehole in the earth comprising a drill string having a drill bit at one end thereof, said drill string including a plurality of sections of drill pipe joined to one another end to end, logging apparatus mounted in the vicinity of said drill bit, and a Signal transmission circuit electrically coupling said logging apparatus through said sections of drill pipe :to surface electrical equipment at the end of said drill string remote from said drill bit, said sections of drill pipe including first and second intercoupled pipe sections, a first coil disposed in said first pipe section at the junction of said first and second pipe sections, a second coil disposed in said second pipe section at the junction of said first and second pipe sections, said first and second coils being arranged to form a transformer coupling between said first and second pipe sections, means for applying a signal to said first coil, semi-conductor amplifying means having an input and an output dispose-d within said second pipe section and utilization means disposed at the end of said second pipe section remote from said first pipe section, the input of said semi-conductor amplifying means being coupled to said second coil and the output of said semiconductor amplifying means being coupled to said utilization means, each of said first and second coils being imbedded in a respective annular unit formed essentially of an epoxy resin, said semi-conductor amplifying means also being imbedded in one of said annular units.

4. Apparatus as set forth in claim 3 wherein said semiconductor amplifying means includes a silicon junction transistor.

5. In a system for drilling a borehole in the earth comprising a drill string having a drill bit at one end thereof, said drill string including a plurality of sections of drill pipe joined to one another end to end, logging apparatus mounted in the vicinity of said drill bit, and a signal transmission circuit electrically coupling said logging apparatus through said sections of drill pipe to surface electrical equipment at the end of said drill string remote from said drill bit, said sections of drill pipe including first and second intercoupled pipe sections, a first coil disposed in said first pipe section at the junction of said first and second pipe sections, a second coil disposed in said second pipe section at the junction of said first and second pipe sections, said first and second coils being arranged to form a transformer coupling between said first and second pipe sections, means for applying a signal to said first coil, a transistor having an emitter, a collector and a base, said second coil being coupled to said transistor between the base and emitter thereof, utilization means disposed at the end of said second pipe section remote from said first pipe section and a source of energy coupled to said transistor between said collector and emitter through said utilization means, wherein said first coil is imbeddcd within a first annular unit formed essentially of an epoxy resin and wherein said second coil and said transistor are imbedded within a second annular unit formed essentially of an epoxy resin.

References Cited in the file of this patent UNITED STATES PATENTS 2,379,800 Hare July 3, 1945 2,414,719 Cloud Jan. 21, 1947 2,659,773 Barney Nov. 17, 1953 2,662,123 Koenig Dec. 8, 1953 2,974,303 Dixon Mar. 7, 1961 FOREIGN PATENTS 1,184,826 France July 27, 1959 OTHER REFERENCES Article The Junction Transistor, Electronics, November 1951, pp. 82-85 (only p 82 relied on).

Herr: Coated-Filler Resin Speeds Encapsulation, Electronics, Aug. 1, 1957, pp. 258-260, 262, 264, 266, 268.

Coblenz: Semiconductor Compounds Open New Horizons Electronics, Nov. 1, 1957, pages 144149. 

1. IN A SYSTEM FOR DRILLING A BOREHOLE IN THE EARTH COMPRISING A DRILL STRING HAVING A FRILL BIT AT ONE END THEREOF, SAID DRILL STRING INCLUDING A PLURALITY OF SECTIONS OF DRILL PIPE JOINED TO ONE ANOTHER END TO END, LOGGING APPARATUS MOUNTED IN THE VICINITY OF SAID DRILL BIT, AND A SIGNAL TRANSMISSION CIRCUIT ELECTRICALLY COUPLING SAID LOGGING APPARATUS THROUGH SAID SECTIONS OF DRILL PIPE TO SURFACE ELECTRICAL EQUIPMENT AT THE END OF SAID DRILL STRING REMOTE FROM SAID DRILL BIT, EACH OF SAID SECTIONS OF DRILL PIPE HAVING A FIRST COIL DISPOSED AT ONE END THEREOF AND A SECOND COIL DISPOSED AT THE OTHER END THEREOF, THE FIRST COIL OF ONE PIPE SECTION AND THE SECOND COIL OF AN ADJACENT PIPE SECTION BEING INDUCTIVELY COUPLED TO ONE ANOTHER THEREBY COMPRISING A TRANSFORMER, CIRCUIT MEANS COUPLING SAID FIRST COIL TO SAID SECOND COIL WITHIN SAID SECTION OF DRILL TAPE, EACH OF SAID CIRCUIT MEANS INLCLUDING A SEMICONDUCTOR AMPLIFIER HAVING AN INPUT COUPLED TO ONE OF SAID COILS AND AN OUTPUT COUPLED TO THE OTHER OF SAID COILS, SAID FIRST COIL AND SAID SEMI-CONDUCTOR AMPLIFIER BEING IMBEDDED WITHIN A FIRST ANNULAR UNIT FORMED ESSENTIALLY OF EPOXY RESIN AND FITTED CLOSELY WITH SAID ONE END OF EACH OF SAID SECTIONS OF DRILL PIPE, AND SAID SECOND COIL BEING IMBEDDED WITHIN A SECOND ANNULAR UNIT FORMED ESSENTIALLY OF EPOXY RESIN AND FITTED CLOSELY WITHIN SAID OTHER END OF EACH OF SAID SECTIONS OF DRILL PIPE. 